bubble_chart Overview

The third ventricle is located between the two thalami and is a longitudinally elongated fissure. Its roof contains the choroid plexus and the internal cerebral veins, while its base consists of the optic chiasm, infundibular recess, tuber cinereum, mammillary bodies, and hypothalamus. The third ventricle communicates with the left and right lateral ventricles via the interventricular foramina and connects to the fourth ventricle through the cerebral aqueduct. It receives cerebrospinal fluid (CSF) from the lateral ventricles, combines it with CSF produced by the choroid plexus of the third ventricle, and directs the flow to the fourth ventricle via the cerebral aqueduct. Tumors of the third ventricle refer to those either originating within the third ventricle or growing into the third ventricle from adjacent structures. Primary tumors of the third ventricle include gliomas, teratomas, epidermoid cysts, and colloid cysts. These account for approximately 3% of intracranial tumors and are more common in children and young adults, with a higher incidence in males than females. Due to their tendency to obstruct CSF circulation pathways, these tumors often lead to increased intracranial pressure, which is a common reason for medical consultation. Tumors that grow into the third ventricle from surrounding areas not only cause increased intracranial pressure by obstructing CSF flow but also exhibit focal neurological signs and symptoms related to the invasion of their original brain tissue, along with distinctive radiographic features.

bubble_chart Clinical Manifestations

Due to the small size of the third ventricle cavity, early-stage tumors are prone to obstruct the cerebrospinal fluid circulation pathway, leading to increased intracranial pressure that gradually worsens. If the tumor is small and has not yet caused obstruction, the patient may not exhibit any obvious symptoms. When the tumor invades the tissues surrounding the third ventricle, focal symptoms may arise.

1. Increased Intracranial Pressure The obstruction caused by the tumor disrupts cerebrospinal fluid circulation, resulting in increased intracranial pressure. Clinically, patients experience severe headache, nausea, and vomiting. The headache may temporarily alleviate with changes in head or body position, likely due to the tumor acting as a valve within the ventricle, temporarily relieving the obstruction and restoring cerebrospinal fluid flow, thereby reducing or stopping the headache. Recurrent obstruction leads to repeated headache episodes, and severe cases may result in unconsciousness or even death. Patients often exhibit forced head and body positions, with most experiencing worsened headaches when lying supine and relief when prone. Consequently, during sleep, seasonal disease patients often adopt a face-down posture to mitigate headache episodes.

2. Focal Symptoms When the tumor invades adjacent brain tissue, corresponding focal symptoms emerge. Depending on the tumor's location and growth direction, manifestations vary, with the most common being symptoms of hypothalamic damage. These include endocrine and metabolic dysfunction, such as changes in sexual function, obesity, dystrophia adiposogenitalis syndrome, and water-salt metabolism disorders, which are also primary symptoms frequently seen in third ventricle tumors. Clinically, this presents as decreased libido, impotence, menstrual irregularities, or amenorrhea; in pediatric cases, precocious puberty may occur. Since the hypothalamus is involved in fat metabolism, abnormal fat distribution and obesity may develop. Some patients exhibit diabetes insipidus, while damage to the appetite center may lead to anorexia or, rarely, hyperphagia. A few patients may experience drowsiness during the disease course. If the tumor extends posteriorly, damaging the midbrain and quadrigeminal bodies, patients may exhibit upward gaze palsy, hearing impairment, and oculomotor nerve paralysis. Third ventricle tumors often disrupt connections between the hippocampus, thalamus, hypothalamus, and mammillary bodies, leading to memory decline and psychiatric changes. When the tumor compresses the brainstem, affecting its blood supply, muscle weakness in the lower limbs may occur, causing patients to experience leg weakness and falls. Tumors in the anterior third ventricle may compress the optic nerves and chiasm, resulting in vision loss and visual field defects. A few patients may experience diencephalic seizures, clinically presenting as nausea, vomiting, sweating, facial flushing, pupil changes, palpitations, and other autonomic symptoms.

3. Fundus Changes The primary fundus changes in patients are optic disc edema caused by increased intracranial pressure, manifesting as blurred disc margins and loss of physiological cupping. Some tumors growing from outside into the third ventricle may directly compress the optic nerves, leading to primary optic atrophy, as seen in craniopharyngiomas and pituitary adenomas. Prolonged intracranial pressure elevation may cause secondary optic atrophy, resulting in vision decline or even blindness.

4. Others Tumors originating outside and growing into the third ventricle exhibit specific clinical manifestations related to their primary sites. For example, craniopharyngiomas and pituitary adenomas cause pituitary dysfunction and visual disturbances. Seasonal disease patients with pinealomas, in addition to hypothalamic damage symptoms, may exhibit specific signs of quadrigeminal body impairment, such as Parinaud syndrome. These patients may have unequal or dilated pupils, genital and secondary sexual characteristic development (precocious puberty), and abnormal skeletal growth.

bubble_chart Auxiliary Examination

1. Skull X-ray plain film Skull plain films of third ventricle tumors only show signs of increased intracranial pressure.

2. Lumbar puncture and cerebrospinal fluid examination The patient has increased intracranial pressure, with elevated protein and sodium levels in the cerebrospinal fluid.

3. Electroencephalography (EEG) Routine EEG examination shows no specific abnormalities, only manifestations of increased intracranial pressure. Damage to midline structures may sometimes exhibit paroxysmal high-amplitude slow waves at 5–7 Hz.

4. Ventriculography This is of particular significance in the examination of third ventricle tumors. Ventriculography reveals symmetrical enlargement of both lateral ventricles, and sometimes the third ventricle may not be visualized. Filling defects and tumor shadows may be observed within the third ventricle. Visualization of the third ventricle depends on whether the interventricular foramen is obstructed.

bubble_chart Differentiation

(1) Pinealoma Pinealoma accounts for 1-2% of intracranial tumors, with a higher incidence in males than females, and most commonly occurs between the ages of 10 and 20. Clinically, it primarily manifests as increased intracranial pressure, symptoms of compression on adjacent tissues, and endocrine disorders. The tumor grows downward, invading the third ventricle or compressing the aqueduct of the midbrain, obstructing cerebrospinal fluid circulation and leading to elevated intracranial pressure. Patients experience headache in the forehead or temporal region. The increase in intracranial pressure often progresses gradually. When the quadrigeminal body is affected, patients may exhibit impaired upward or downward conjugate eye movements, dilated pupils, or unequal pupil sizes. Some may also experience eyelid ptosis, hearing loss, or tinnitus. If the brainstem or cerebellar peduncles are involved, patients may develop pyramidal tract signs and ataxia, though these symptoms generally appear later. Endocrine disorders are observed only in male children, presenting as precocious puberty and skeletal abnormalities. Skull X-rays often reveal enlarged calcification of the pineal gland. Ventriculography shows lateral and third ventricular enlargement, a filling defect in the posterior third ventricle, and anterior displacement of the aqueduct of the midbrain. Cerebral angiography may indicate elevation of the great cerebral vein.

(2) Craniopharyngioma Craniopharyngioma is a tumor derived from embryonic remnants, commonly located in the suprasellar region and frequently seen in children. Clinically, it primarily presents as: ① Symptoms of increased intracranial pressure: Patients experience headache, nausea, vomiting, decreased vision, and diplopia. ② Endocrine disturbances: Patients exhibit hypogonadism, manifested as decreased libido, impotence, or amenorrhea. In children, growth and development are delayed, resulting in a childlike appearance despite reaching adulthood, though intellectual development remains unaffected. Additionally, about 32% of patients develop polydipsia and polyuria, or even diabetes insipidus. A few patients may experience abnormal fat distribution leading to obesity. ③ Visual field and acuity changes: Due to compression of the optic nerve, patients experience vision loss and visual field defects, with bitemporal hemianopia being the most common. Optic disc edema or primary optic atrophy may occur. Skull X-rays revealing calcification in or above the sella turcica further support the diagnosis of craniopharyngioma. Differentiation from third ventricular tumors is straightforward.

(3) Chromophobic Pituitary Adenoma Chromophobic pituitary adenoma originates from the chromophobe cells of the pituitary gland and is more prevalent in adults aged 20-50. Clinically, it presents as: ① Pituitary dysfunction: Manifested as decreased libido, impotence, reduced facial and pubic hair, and, in severe cases, testicular atrophy. In women, menstrual cycles lengthen or cease, and patients may gradually develop obesity, lethargy, and low basal metabolic rates. A few patients may experience polydipsia and polyuria. ② Visual field and acuity impairment: About two-thirds of patients experience progressive vision loss, often starting in one eye before affecting the other, eventually leading to blindness. Nearly all patients exhibit visual field defects, mostly bitemporal hemianopia, followed by unilateral temporal hemianopia with contralateral blindness or normal vision. Some patients may even lose vision in both eyes. ③ Primary optic atrophy: Initially, the optic disc appears pale, progressing to a silvery-white and then pallid appearance as compression worsens, accompanied by gradual vision loss until blindness. ④ Two-thirds of patients experience headache, typically dull and persistent, located in the bitemporal or frontal regions, without nausea or vomiting. ⑤ Skull X-rays reveal spherical or basin-shaped enlargement of the sella turcica, and brain CT scans can visualize the tumor mass.

(IV) Brainstem Tumors All patients have grade I intracranial hypertension. For midbrain tumors, especially those located in the tegmentum, symptoms of intracranial hypertension appear early and are more pronounced. Most patients exhibit altered consciousness and mental disorders. Due to damage to the brainstem reticular formation, patients may present with drowsiness, apathy, and even hallucinations. A slowly progressive crossed paralysis is a prominent feature of brainstem tumors, often accompanied by multiple cranial nerve impairments in seasonal disease patients. In the advanced stage, cerebrospinal fluid examination may reveal elevated intracranial pressure and increased protein content. Pneumoencephalography shows enlargement of the lateral and third ventricles, particularly more pronounced in midbrain tumors. Sometimes, a filling defect in the posterior part of the third ventricle may be observed. In some patients, cerebral angiography may reveal deformation and displacement of the posterior cerebral artery pulse, superior cerebellar artery pulse, and basilar artery pulse.

(5) Saddle tubercle meningioma: Patients often present with visual impairment and headache as the initial symptoms, accompanied by visual field defects. Visual impairment usually starts in one eye first, then spreads to the other eye, commonly manifesting as bitemporal hemianopia or blindness in one eye with temporal hemianopia in the other. The optic nerve shows primary atrophy, while secondary atrophy is rare. Endocrine disorders manifest as decreased libido, impotence, and amenorrhea. Some patients may also experience olfactory hallucinations, oculomotor nerve palsy, and hemisensory disturbances. Skull X-ray films generally show no changes in the sella turcica, with only a few patients exhibiting a shortened dorsum sellae. Cerebral angiography reveals upward and backward displacement of the root of the anterior cerebral artery, often with an enlarged ophthalmic artery diameter and branches extending toward the saddle tubercle to supply the tumor.

(6) Intraventricular hematoma: This mostly occurs in elderly individuals, as arteriosclerosis makes blood vessels prone to rupture after craniocerebral trauma, leading to intraventricular hematoma. Patients typically have a history of craniocerebral trauma, presenting with deep unconsciousness and a sharp increase in intracranial pressure after the injury. Patients may quickly develop bilateral pyramidal tract signs, dilated or constricted pupils, irregular breathing, and decerebrate rigidity. Generally, there are no localized signs, but meningeal irritation symptoms are prominent, and sometimes symptoms of autonomic dysfunction may appear. Lumbar puncture reveals increased cerebrospinal fluid pressure and a bloody appearance. Cerebral angiography shows ventricular enlargement, and brain CT scans display localized high-density images in the ventricles.